Name simple aliphatic compounds with A Level groups
Choose the longest suitable carbon chain and apply systematic names to simple aliphatic A Level compounds within the syllabus limits.
Section 29 · An introduction to A Level organic chemistry
A Level; Cambridge International Chemistry 9701, 2028–2030 syllabus, Topic 29. Follow the formula, naming and optical-isomerism limits stated in the syllabus. Benzene-ring displayed formulas are not expected; use the supplied convention for aromatic skeletal formulas. Do not extend the optical-isomerism scope to naming diastereoisomers or meso compounds. Written practice is self-checked
Before you begin
- Use covalent formula conventions, functional groups, reaction terminology, and the AS organic chemistry foundations.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
In a simple carboxylic-acid name, where does numbering start?
What you will learn
- Choose and number the parent chain
- Name acyl chlorides, amides and amino acids using the stated simple-molecule scope
- Apply locants and prefixes without naming secondary or tertiary amines beyond the syllabus requirement
Choose the parent and locate the principal group
For a simple aliphatic compound, select the longest suitable chain that contains the principal functional group, then number it to give the group and substituents the lowest valid locants. Keep the carbonyl carbon in the parent count for an acyl chloride or amide.
Acyl chlorides use the corresponding alkanoyl chloride name: CH₃CH₂COCl is propanoyl chloride. Primary amides use alkanamide names: CH₃CH₂CONH₂ is propanamide. A simple amino acid such as H₂NCH₂COOH is 2-aminoethanoic acid.
Keep the published boundaries visible
The syllabus expects systematic names for simple aliphatic compounds with the listed groups, up to six carbon atoms. It includes cyclic compounds with one ring of up to six carbons. Esters and amides may extend to six plus six carbon atoms; the syllabus restricts ester and nitrile naming examples to straight chains.
The page 47 table states that naming secondary and tertiary amines is not required. Do not infer that all detailed substituent conventions or complex polycyclic naming are examined from this introduction.
Pause and explain
What is the correct name for CH₃CH₂CONH₂?
Worked example
Name CH₃CH₂CH(NH₂)COOH.
Show the worked solution
- The parent chain includes the carboxyl carbon: four carbons total.
- Number from the carboxyl carbon, which is carbon 1.
- The amino group is on carbon 2.
Answer 2-aminobutanoic acid.
Try a topic test
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Name CH₃CH₂COCl.
Give me a hint
Count the carbonyl carbon as part of the chain.
Compare my reasoning
- The chain has three carbons including C=O.
- The functional group is an acyl chloride.
- Use the propanoyl chloride name.
Propanoyl chloride.
Look for these in your work
- Three-carbon parent identified
- Acyl chloride recognized
- Name formed
Name HOOCCH₂CH₂NH₂.
Give me a hint
Number from the carboxyl carbon and locate –NH₂.
Compare my reasoning
- There are three carbons including the carboxyl carbon.
- The amino group is on carbon 3.
- Use the carboxylic-acid suffix.
3-aminopropanoic acid.
Look for these in your work
- Parent length correct
- Numbering correct
- Amino locant and acid suffix used
A student names CH₃CH₂CH(NH₂)COOH as 3-aminobutanoic acid. Diagnose the error and correct it.
Give me a hint
Number the chain from the carboxyl carbon.
Compare my reasoning
- The acid carbon is carbon 1.
- Moving along the chain, the adjacent carbon is carbon 2.
- The amino group is therefore on carbon 2.
The student numbered from the wrong end. The correct name is 2-aminobutanoic acid.
Look for these in your work
- Correct numbering origin
- Amino locant corrected
- Systematic name supplied
Common mistakes
- Leaving the carbonyl carbon out of the parent-chain count
- Numbering from the wrong end when a carboxyl group is present
- Calling a primary amide an amine
- Extending naming requirements beyond the table's limits
What can you explain now?
In a simple carboxylic-acid name, where does numbering start?
Compare with the explanation
At the carboxyl carbon
The carboxyl carbon is carbon 1 of the parent chain.
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Make it stick
Which naming choices determine the parent and locant in a simple amino acid or acyl chloride?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.